Here is another source.. the CIA's website even lists it.
http://www.cia.gov/cia/publications/...elds/2098.html
You have to scroll down to the bottom of that page.. but here is what it says.
"Chinese, Mandarin 14.37%, Hindi 6.02%, English 5.61%, Spanish 5.59%, Bengali 3.4%, Portuguese 2.63%, Russian 2.75%, Japanese 2.06%, German, Standard 1.64%, Korean 1.28%, French 1.27% (2000 est.)"
That is percentage of the world's population that speaks whatever language.